1. Field of the Invention
The present invention relates to a vehicle starting clutch control device in which the transmission torque capacity of a starting clutch can arbitrarily be controlled by an actuator.
2. Description of the Related Art
Conventionally, disclosed as a control device of this type in JP-B-6-67695 is a vehicle starting clutch control device for controlling an actuator so that the transmission torque capacity of a starting clutch becomes a value required to transmit a torque equal to an engine absorption torque corresponding to the then engine speed at the time of power-off running where the accelerator pedal is not substantially depressed. According to this control device, being different from a control device in which the starting clutch is kept in a complete engaged condition at the time of power-off running as well as power-on running, the starting clutch can be momentarily disengaged so as to prevent the engine stall when the brakes are applied abruptly.
With the aforesaid conventional control device, when the accelerator pedal is depressed abruptly during power-off running the transmission torque capacity of the starting clutch is controlled to gradually increase in order to shift the starting clutch to a completely engaged condition. However, the output torque of the engine does not build up as soon as the accelerator pedal is depressed, and the transmission torque capacity of the starting clutch has increased to some extent during this delay of response. Then, in a case where the above conventional art is applied to the control of a starting clutch for a normal manual transmission which comprises a mechanical friction clutch, drive torque for the drive wheels builds up abruptly through transmission of torque via the starting clutch when the output of the engine builds up, whereby there may be a risk that surging vibrations (longitudinal vibrations) are generated in the body of the vehicle.
The present invention was made in view of the above situation, and an object thereof is to provide a vehicle starting clutch control device which can prevent the generation of surging vibrations when the accelerator pedal is abruptly depressed during power-off running.
With a view to attaining the object, according to the invention, there is provided a vehicle starting clutch control device for arbitrarily controlling a transmission torque capacity of a starting clutch through an actuator, said vehicle starting clutch control device comprising:
first control means for controlling said actuator so that said starting clutch is put in a state in which said starting clutch completely transmits the output torque of an engine at the time of power-on running with an accelerator pedal being depressed;
second control means for controlling said actuator so that the transmission torque capacity of said starting clutch becomes a value required to transmit a torque equal to an engine absorption torque corresponding to the engine speed at the time of power-off running without said accelerator pedal being depressed;
third control means for controlling said actuator so that the transmission torque capacity of said starting clutch gradually increases to shift said starting clutch to a state in which said starting clutch completely transmits the output torque of said engine when said accelerator pedal is depressed during power-off running; and
delay means for delaying the start of control based on said third control means until a predetermined time after said accelerator pedal is depressed.
According to the aspect of the invention, the time when the third control means starts to control to gradually increase the transmission torque capacity of the starting clutch is delayed from the timing when the accelerator pedal is depressed. Therefore, even if there is a delay in building up of the output torque of the engine, the transmission torque capacity of the starting clutch has not increased as high as the conventional art when the output torque of the engine actually builds up, and there is produced a slippage in the starting clutch. Thereafter, as the transmission torque capacity of the starting clutch increases, of the output torque of the engine, the ratio of output torque which is to be transmitted to the drive wheels via the starting clutch is increased. Consequently, even if the accelerator pedal is abruptly depressed during power-off running, the drive torque of the drive wheels is allowed to build up moderately, whereby the generation of surging vibrations is prevented. The predetermined time may be determined depending upon time that has elapsed since the accelerator pedal is depressed, or time may be determined as the predetermined time when a detected engine output torque exceeds the transmission torque capacity of the starting clutch.
Incidentally, the engine absorption torque is equal to a torque required to drive the engine reversely and varies depending upon the engine speed. The engine absorption torque also varies depending upon engine temperature, the adaptability of the engine, oil volume, oil type, oil level inclination and the like, and therefore it is difficult to set an accurate value. Due to this, in the conventional art, it is presumed that the transmission torque capacity of the starting clutch during power-off running is controlled to be a value which is higher by some extent than the reference value of the engine absorption torque corresponding to the engine speed, for example, a value obtained by multiplying the reference value by a relatively large safety factor, so that there is produced no slippage in the starting clutch even when the actual value of the engine absorption torque exceeds slightly the reference value. This is because when a smaller safety factor is used, the actual value of the engine absorption torque exceeds the transmission torque capacity of the starting clutch, and a slippage is likely to be generated in the starting clutch, leading to a further risk that the effect of engine braking is reduced or the durability thereof is deteriorated. Thus, a larger safety factor needs to be adopted. As a result, the transmission torque capacity of the starting clutch at the time of power-off running becomes relatively large, and the disengagement of the starting clutch is delayed when the brakes are applied abruptly, leading to a risk that the engine stalls.
To cope with this, the second control means is constructed to control the actuator by setting as a control target value a control amount of the actuator in which the transmission torque capacity of the starting clutch becomes equal to a set value for the engine absorption torque which is a value obtained by multiplying a reference value of the engine absorption torque corresponding to the engine speed by a predetermined safety factor, detecting the specific slippage of the starting clutch and feedback correcting the control target value such that the specific slippage becomes equal to or less than a predetermined value. According to this construction, even if a relatively small safety factor is adopted, there should be produced no excessive slippage which is not good to the starting clutch. As a result, the transmission torque capacity of the starting clutch at the time of power-off running can be suppressed to a required minimum of limit, whereby the drawback inherent in the conventional art can be prevented.
Incidentally, while it is considered that the transmission torque capacity of the starting clutch is maintained to a value just before the accelerator pedal is depressed until the control by the third control means is started, in order to ensure that the occurrence of surging vibrations is prevented, the transmission torque capacity when the third control means starts to control should be made as low as possible. To cope with this, the delay means is preferably constructed to start the control by the third control means after the transmission torque capacity of the starting clutch is maintained to a value corresponding to the engine absorption torque resulting when the engine speed is around 1000 rpm for a predetermined time after the accelerator pedal is depressed.
Note that in an embodiment of the invention which will be described later, step S2 shown in FIG. 4 corresponds to the first control means, steps S4 to S6, S11 and S12 in FIG. 4 to the second control means, and steps S18, S19 in FIG. 4 to the third control means, and steps S14 to S17 in FIG. 4 to the delay means.